Conventionally, a device has been known that detects the charged state of a battery that is installed in a vehicle or the like, and can be charged and discharged (see, for example, Patent Document 1). The device described in this Patent Document 1 detects a relative charged state by applying time-accumulation to charge and discharge currents detected by a current sensor, or an absolute charged state as the remaining capacity of the battery, based on the charge and discharge currents detected by the current sensor and voltage values. Then, the device executes charge control to charge the battery, by controlling the amount of power generation based on the detected charged states.